Manfred Stöckler

Quantum Field Theory

Quantum field theory (QFT) shares many of its philosophical problems with quantum mechanics. This applies in particular to the quantum measurement process and the connected interpretive problems, to which QFT contributes hardly any new aspects, let alone solutions. The question as to how the objects described by the theory are spatially embedded was already also discussed for quantum mechanics. However, the new mathematical structure of QFT promises new answers, which renders the spatiotemporal interpretation of QFT the pivotal question. In this chapter, we sketch the mathematical characteristics of QFT and show that a particle as well as a field interpretation breaks down.

Philosophen in der Mikrowelt — ratlos?

SummaryIn this report on the present state of the discussion about the interpretation of quantum mechanics an attempt is made to provide an idea of the philosophical relevance of the foundations of physics. A simplified model of the measuring process is given which shows the difficulties in the interpretation of quantum mechanics. It is argued against Bohrs solution (also in a version of H. Putnam). Two examples show possible philosophical consequences of quantum mechanics: The variety of quantum logics challenges the foundations of logic, the paradox of Einstein, Podolsky and Rosen (with Bells inequality) may be interpreted along the lines of holism. Against alleged refutations of realism by means of quantum mechanics, a realist standpoint is maintained. A proper interpretation of quantum mechanics from an epistemological point of view seems still to be lacking.In my childhood the legend was current, that only twelve men in the World understood Einsteins theory. Nowadays, relativity is quite tame; but I shall argue presently thatnobody yet understands the quantum theory.Howard Stein

Entanglement and Non-locality: EPR, Bell and Their Consequences

Entangled states are a specific feature of quantum physics that neither have a counterpart in classical physics nor in the realm of our ordinary experiences. In this chapter we outline the debate about these particular states both historically and systematically. We delineate how the debate originated in an argument for the incompleteness of quantum mechanics by Einstein, Podolsky and Rosen, and we show why, on the one hand, the argument is not considered convincing today, on the other hand, however, still affects present discussions. In a second part we give a systematic overview over the contemporary debate on entanglement which focusses on Bell’s theorem and its consequences. Discerning different levels, we reconstruct the theorem and its premises in a clear way and discuss possible consequences. We analyze in detail the received view that Bell’s theorem implies non-locality and relate it to concepts such as “non-separability” and “holism”. Especially we examine the question whether the phenomena involving entangled systems can be explained causally and whether the central conflict between a non-locality and the theory of relativity can be solved.

Verschränkung und Nicht-Lokalität: EPR, Bell und die Folgen

Die Probleme, die wir in diesem Kapitel diskutieren, haben ihren formalen Ursprung in der Art und Weise, wie in der Quantentheorie zusammengesetzte Systeme beschrieben werden (vgl. Abschn. 3.1.2).